Not Applicable.
Not Applicable.
This invention relates to a mirror substrate, a mirror with such a mirror substrate, and a production process therefor, and also an EUV projection exposure device therewith.
1. Field of the Invention
Monocrystalline silicon is a preferred substrate material for robust mirrors with a high thermal loading and best shape stability.
For applications in the X-ray region, in particular for soft X-radiation, also termed xe2x80x9cextreme ultravioletxe2x80x9d (EUV), extremely smooth surfaces with micro-roughness values in the angstrom range are required This is attained with so-called xe2x80x9csuper-polishxe2x80x9d.
It has been found by experience that silicon substrates can be homogeneously polished to this standard only poorly or not at all homogeneously over sufficiently large surfaces, particularly in the case of strongly curved surfaces.
2. Discussion of Relevant Art
The preferred application of such EUV mirrors is in EUV lithography, for the mirrors of illumination, mask and projection objective. Their quality of polishing is then decisive for the usability of the whole system. This follows, e.g., from K. Hoh, Bull. Electrotechn. Lab. 49, No. 12, October 1985, pp. 47-54; T. E. Jewell et al., Proc. SPIE, Vol. 1527 (1991); and David M. Williamson, OSA IODC Conference Paper LWA 2-1, pp. 181-184, Jun. 10, 1998.
An X-ray mirror is known from Japanese Patent Document JP-B2-96/032 592, in which a matrix with sintered SiC is coated with crystalline SiC, by which means a precisely smooth surface is obtained.
The invention has as its object the provision of a mirror substrate which combines the positive properties of the silicon single crystal substrate with outstanding xe2x80x9csuper-polishxe2x80x9d properties.
This object is attained by a mirror substrate of crystal, wherein an amorphous cover layer is applied to the substrate, and the amorphous cover layer is covered with a multilayer reflecting layer. According to the invention, a thin, amorphous layer, e.g. of quartz glass, amorphous SiO2, or Al2O3, is applied to a substrate member consisting of a crystal with low thermal expansion and high thermal conductivity (diamond, BN, SiC, silicon, as examples). A cover layer which is known to be well suited for xe2x80x9csuper-polishxe2x80x9d is thereby prepared, without impairing the other properties of the substrate.
The invention also includes the following advantageous features:
The substrate consists of at least one of the following materials: diamond, BN, SiC, or silicon.
The cover layer consists of at least one of the following amorphous materials: quartz glass, SiO2 or Al2O3.
The amorphous cover layer has a thickness in the range of 1 xcexcm through 100 xcexcm.
The micro-roughness of the amorphous cover layer is in the angstrom range.
The multilayer reflection layers are constituted for a wavelength region of 10 nm-20 nm, preferably 13 nm.
The mirror has a curved surface.
In a preferred production process for such a mirror, a substrate of crystal is shaped close to the final contour, an amorphous cover layer is deposited on the mirror side of the substrate, then an optical final polishing takes place and then a multilayer reflecting layer is applied.
Advantageously, the amorphous cover layer is deposited by means of CVD.
Advantageous application of mirrors according to the invention in EUV projection exposure devices comprises an EUV projection exposure device with an EUV source, an illuminating optics, a mask, a projection objective, and a wafer, wherein at least one mirror according to the invention is contained in the illuminating optics or in the projection objective.